Heretofore, there have often been problems in thermoplastic resins for use in electrophotographic photoreceptors (specifically, organic photoreceptors) such that sufficient transferability at a high temperature could not be achieved in high humidity environment or photoreceptors frequently became scratched therein, resulting in uneven half-tone images. To overcome such problems, there was attempted improvement by an electrophotographic photoreceptor provided with a protective layer, in which enhancement of the surface hardness of a photoreceptor was attempted through a curing reaction, as described in, for example, JP-A No. 8-179541 (hereinafter, the term JP-A refers to Japanese Patent Application Publication). However, a progress of the curing reaction was insufficient and image deletion in unreacted sites was caused, or resistance to abrasion or scratch was insufficient due to lowering in mechanical strength, so that a photoreceptor exhibiting stable electrophotographic characteristics could not be obtained.
In response to the foregoing problems, there was an attempt of dispersive-mixing metal oxide particles to control the resistance of a protective layer to inhibit lowering of the surface resistance, as described in JP-A No. 5-173350, or an attempt of addition of metal oxide particles exhibiting a hydrophobicity degree of 50 or more to prevent image deletion, as described in JP-A No. 2000-010821.
However, addition of metal oxide particles exhibiting a hydrophobicity degree of 50 or more to a protective layer containing a curing compound was insufficient to prevent image deletion under high temperature and high humidity, due to water or corona discharge by-products such as NOx. Further, the surface layer durability was deficient and satisfactory performance was not achieved in resistance to abrasion or scratch. It is assumed to be due to that metal oxide particles disadvantageously act for reactivity of such a curing compound.
As set forth above, it is the current status that compatibility of resistance and image characteristics cannot be achieved only by the conventional technology and essential solution for these problems has not yet realized.